Method for culturing mesenchymal stem cells

ABSTRACT

Disclosed is a method for culturing mesenchymal stem cells, comprising culturing mesenchymal stem cells in a medium containing calcium in a concentration of from 2.1 to 3.8 mM and magnesium in a concentration of from 1.0 to 3.0 mM under a hypoxic condition of 2 to 5% oxygen. The culturing method can increase the population of mesenchymal stem cells even with a small number of passages by improving mesenchymal stem cells in proliferative capacity and viability. In addition, the mesenchymal stem cells prepared by the culturing method are effectively used to treat or improve a pulmonary disease.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No. 15/403,457filed Jan. 11, 2017, now U.S. Pat. No. 10,294,456 issued May 21, 2019,which is a Continuation of U.S. application Ser. No. 14/425,220 filedMar. 2, 2015, now U.S. Pat. No. 9,580,687 issued Feb. 28, 2017, which isa National Stage Application under 35 U.S.C. § 371 of InternationalApplication No. PCT/KR2013/007891, filed on Sep. 2, 2013, and claims thebenefit of Korean Application No. 10-2012-0097193 filed on Sep. 3, 2012in the Korean Patent Office, the disclosures of which are incorporatedherein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to a method for culturing mesenchymal stemcells with efficiency.

BACKGROUND OF THE INVENTION

The term “stem cell” is a generic name for an undifferentiated type ofbody cell found in tissues of embryos, fetuses and adults, which has thepotential of differentiating into a diverse range of specialized celltypes. Stem cells are characterized by self-renewal, the ability to gothrough numerous cycles of cell division (while maintaining anundifferentiated state), and potency, the capacity to differentiate intospecialized cell types in response to certain stimuli (environment), andeven by plasticity, the ability to cross lineage barriers and adopt theexpression profile and functional phenotypes of cells that are unique toother tissues.

Stem cells may be classified according to various criteria. Potencyallows the classification of stem cells: pluripotent stem cells,multipotent stem cells and unipotent stem cells. Pluripotent stem cellshave pluripotency to differentiate into any type of cells. Embryonicstem cells and induced pluripotent stem cells (iPS), which have recentlyreceived intensive attention from scientists, are representative ofpluripotent stem cells. Adult stem cells show multipotency orunipotency. Among them are hematopoietic stem cells, mesenchymal stemcells, neural stem cells, etc.

In spite of various attempts to utilize the pluripotency of humanembryonic stem cells in cell therapeutics, the high likelihood ofoncogenesis and immune rejection response still remain and are difficultobstacles to overcome.

Induced pluripotent stem cells (iPS cells) have recently been suggestedas a solution to these problems. iPS cells are a type of pluripotentstem cell artificially derived from a differentiated adult somatic cellby reprogramming. iPS cells may avoid the issue of immune rejectionresponse because they are derived entirely from the patient, however,the risk of oncogenesis with iPS cells is still a problem to be solved.

As an alternative, mesenchymal stem cells are being promoted becausethey exhibit immunomodulatory effects and present no risk ofoncogenesis. Mesenchymal stem cells are multipotent stem cells that candifferentiate into a variety of cell types, including adipocytes,osteoblasts, chondrocytes, myoblasts, neuroblasts, myocardioblasts,hepatocytes, islet beta cells, vascular cells, etc., and are known tohave the function of modulating immune responses.

Mesenchymal stem cells may be isolated from various tissues such as thebone marrow, umbilical cord blood, adipose tissue, etc., but are notsufficiently defined because cell surface markers are somewhat differentfrom one another according to the origin from which the mesenchymal stemcells are derived. On the whole, if they can differentiate intoosteoblasts, chondrocytes and myoblasts, have a spindle shapedmorphology, and express the surface markers CD73(+), CD105(+), CD34(−)and CD45(−), the stem cells are defined as mesenchymal stem cells. Inthis context, mesenchymal stem cells of different genetic origins and/orbackgrounds do not significantly differ from one another in terms oftheir definition, i.e., that of a mesenchymal stem cell, but aretypically different from each other in terms of in vivo activity.Further, when mesenchymal stem cells are used as exogenous celltherapeutics, a limited pool of mesenchymal stem cells does not allowmany choices or available options, even in spite of low in vivoactivity.

In addition, the minimum number of mesenchymal stem cells necessary forthem to be used as a cell therapeutic in regenerative medicine and/orcell therapy is approximately 1×10⁹ cells. In practice, the minimumnumber is further increased in consideration of experiments for settingproper conditions and determining criteria. The supply of mesenchymalstem cells in such quantities from various origins requires at least tenin vitro passages. In this case, however, the cells become aged anddeformed so that they may be unsuitable for use as cell therapeutics.

Thus, a culturing method effective for the mass production ofmesenchymal stem cells is required.

Methods for culturing mesenchymal stem cells are described in KoreanPatent Laid-Open Publication No. 2003-0069115, and literature [PittingerM F et al. Science, 284: 143-7, 1999; Lazarus H M et al. Bone MarrowTransplant, 16: 557-64, 1995; and Kern et al., Stem Cells, 24:1294-1301, 2006], but difficulties were found in guaranteeing the numberof cells available for mass production. In addition, these methodssuffer from the disadvantage of a decreasing number of mesenchymal stemcells in proliferative capacity every passage. For example, umbilicalcord blood-derived mesenchymal stem cells cannot proliferate, but arerapidly aged after 9˜10 passages, and this phenomenon is found after 5˜6passages in bone marrow- or lipid-derived mesenchymal stem cells.Therefore, there is a need for a novel method by which the number ofmesenchymal stem cells can be increased to the extent sufficient forindustrial applicability with higher simplicity and economical benefitcompared to conventional methods.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a methodfor culturing mesenchymal stem cells with efficiency.

It is another object of the present invention to provide mesenchymalstem cells, prepared by the method, that exhibit excellent proliferativecapacity and immunological properties.

It is a further object of the present invention to provide a celltherapeutic agent comprising the mesenchymal stem cells.

In accordance with one aspect of the present invention, there isprovided a method for culturing mesenchymal stem cells, comprisingculturing mesenchymal stem cells in a medium containing calcium in aconcentration of from 2.1 to 3.8 mM and magnesium in a concentration offrom 1.0 to 3.0 mM under a hypoxic condition with a 2˜5% oxygenconcentration.

In accordance with another aspect of the present invention, there isprovided mesenchymal stem cells, prepared by the method, which areimproved in proliferative capacity, viability, recovery rate, and immuneproperty.

In accordance with further aspect of the present invention, there isprovided a cell therapeutic agent comprising the mesenchymal stem cellsof the present invention.

The culturing method of the present invention can increase thepopulation of mesenchymal stem cells even at a small number of passagesby improving mesenchymal stem cells in proliferative capacity andviability. In addition, the mesenchymal stem cells prepared by theculturing method of the present invention are effectively used not onlyas a safe cell therapeutic agent due to their lacking immunogenicity,but also as a cartilage regenerating medicine owing to their excellentsecretion of cytokines.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A, FIG. 1B, FIG. 1C, and FIG. 1D are graphs showing cell countfolds relative to the seeded cell count at 7 days (FIG. 1A and FIG. 1C)and cumulative cell counts until 21 days (FIG. 1B and FIG. 1D) afterumbilical cord blood-derived mesenchymal stem cells derived from twodifferent sources (MSC #1 and #2) were cultured in α-MEM ranging incalcium concentration from 1.8 to 9.3 mM. In FIG. 1A and FIG. 1C, P1 toP3 represent numbers of passage.

FIG. 2A, FIG. 2B, FIG. 2C, and FIG. 2D are graphs showing cell countsafter umbilical cord blood-derived mesenchymal stem cells derived fromtwo different sources (MSC #1 and #2) were cultured for 7 days in thepresence of a total calcium concentration of from 1.8 to 3.6 mM (FIG. 2Aand FIG. 2C) and for 6 days in the presence of a total calciumconcentration of from 1.8 mM to 4.4 mM (FIG. 2B and FIG. 2D).

FIG. 3A, FIG. 3B, FIG. 3C, and FIG. 3D are graphs showing doubling timeswhen umbilical cord blood-derived mesenchymal stem cells derived fromtwo different sources (MSC #1 and #2) were cultured under various oxygenconditions (normal, 3% and 5%) (FIG. 3A and FIG. 3C), and cumulativecell counts until 21 days after the umbilical cord blood-derivedmesenchymal stem cells were cultured under the oxygen conditions (FIG.3B and FIG. 3D). In FIG. 3A and FIG. 3C, P1 to P3 represent numbers ofpassage.

FIG. 4A and FIG. 4B show doubling times (FIG. 4A), and cumulative cellcounts (FIG. 4B) after umbilical cord blood-derived mesenchymal stemcells (MSC #1) were cultured in a typical condition (control), in anincreased calcium condition (Ca²⁺), in a hypoxic condition, and in a CMHcondition. In each of FIG. 4A and FIG. 4B, P5 to P12 represent numbersof passage, and the CMH condition means a combination of the calcium andmagnesium addition condition and the hypoxic condition.

FIG. 5A and FIG. 5B show cell viability (FIG. 5A) and recovery rates(FIG. 5B) 1 and 2 days after umbilical cord blood-derived mesenchymalstem cells were cultured in a typical condition (control), in a calciumaddition condition (Ca²⁺), in a hypoxic condition, and in a CMHcondition.

FIG. 6A, FIG. 6B, FIG. 6C, and FIG. 6D show doubling times (FIG. 6A andFIG. 6C), and cumulative cell counts (FIG. 6B and FIG. 6D) afterumbilical cord blood-derived mesenchymal stem cells (MSC #1 to #4) werecultured in a typical condition (control), and in a CMH condition. Ineach of FIGS. 6A-6D graph, P1 to P9 represent numbers of passage.

FIG. 7A and FIG. 7B show mRNA expression levels of the stemness markersOct4 and nanog and the senescence marker P16 after umbilical cordblood-derived mesenchymal stem cells derived from two different sources(MSC #1 and #2) were cultured in a typical condition (control), in acalcium addition condition (Ca2+), in a hypoxic condition, and in a CMHcondition.

FIG. 8A and FIG. 8B show photographs of umbilical cord blood-derivedmesenchymal stem cells stained with SA-β-gal after passages in a typicalcondition (control) and in a CMH condition (FIG. 8A), and a graph inwhich β-gal activity is plotted according to culture conditions afterumbilical cord blood-derived mesenchymal stem cells were cultured in atypical condition (control), in a calcium addition condition (Ca²⁺), ina hypoxic condition, and in a CMH condition (FIG. 8B).

FIG. 9A and FIG. 9B show photographs of umbilical cord blood-derivedmesenchymal stem cells derived from two different sources (MSC #1 and#2) after the cells cultured in a typical condition (control) and in aCMH condition were induced to differentiate to cartilage and bone.

FIG. 10A and FIG. 10B show graphs illustrating whether two differentumbilical cord blood-derived mesenchymal stem cells (MSC #1 and #2)cultured in a typical condition (control) and in a CMH conditionstimulate responding cells (A), wherein A, B and H represent respondingcells, stimulator cells, and PHA, respectively.

FIG. 11A and FIG. 11B show graphs of levels of PGE₂ (prostaglandin E₂)released from umbilical cord blood-derived mesenchymal stem cells (MSC#1 and #2) cultured in the conditions of FIG. 10A and FIG. 10B.

FIG. 12 is a graph showing levels of Tsp-2 released from four differentumbilical cord blood-derived mesenchymal stem cells (MSC #1 to #4)cultured for 24 hrs in a typical condition (control) and in a CMHcondition.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with a preferred embodiment, the present inventionprovides a method for culturing mesenchymal stem cells, comprisingculturing mesenchymal stem cells in a medium containing calcium in aconcentration of from 2.1 to 3.8 mM and magnesium in a concentration offrom 1.0 to 3.0 mM under a hypoxic condition of 2 to 5% oxygen.

The culturing method of the present invention may be applied tomesenchymal stem cells of various origins. Examples of the mesenchymalstem cells useful in the present invention include those derived fromumbilical cord blood, bone marrow, lipid, muscle, skin, amniotic fluid,umbilical cord, or teeth, but are not limited thereto. In one preferredembodiment of the present invention, the culturing method of the presentinvention is applied to umbilical cord blood-derived mesenchymal stemcells.

In addition, the mesenchymal stem cells to which the culturing method ofthe present invention can be applied may be derived from varioussubjects. For example, the mesenchymal stem cells useful in the presentinvention may be obtained from mammals including humans, but are notlimited thereto. In one preferred embodiment of the present invention,mesenchymal stem cells of human origin are used.

The culturing method of the present invention is primarily characterizedby the use of a culture medium containing calcium in a concentration offrom 2.1 to 3.8 mM, and magnesium in a concentration of from 1.0 to 3.0mM. The culture medium may be prepared from a typical culture medium forstem cells by adjusting the concentrations of calcium and magnesium.Examples of the typical culture medium include Dulbecco's modified eaglemedium (DMEM), minimal essential medium (MEM), α-MEM, McCoys 5A medium,eagle's basal medium, CMRL (Connaught Medical Research Laboratory)medium, Glasgow minimal essential medium, Ham's F-12 medium, IMDM(Iscove's modified Dulbecco's medium), Leibovitz's L-15 medium, RPMI(Roswell Park Memorial Institute) 1640 medium, medium 199, and Hank'smedium 199, but are not limited thereto.

Optionally, the culture medium may or may not contain serum. Inaddition, a serum replacement may be used, instead of serum, in theculture medium.

In one embodiment of the present invention, the culture medium contains5 to 30% of fetal bovine serum (FBS). In another embodiment, the culturemedium contains a serum replacement. In addition to a commerciallyavailable product, various growth factors in a human serum or a humanplatelet lysate, including PDGF, TGF, IGF, and cytokines of a family ofsuch proteins may be used as the serum replacement.

In the culturing method of the present invention, calcium functions topromote the proliferation of mesenchymal stem cells, with thesuppression of immunogenicity and the stimulation of cytokine secretion.In this regard, calcium may be used in a concentration of from 2.1 to3.8 mM in the medium, preferably in a concentration of from 3.3 to 3.8mM, and more preferably in a concentration of approximately 3.6 mM. Forinstance, when α-MEM is adopted as the culture medium, calcium may beadded in a concentration of from 0.3 to 2.0 mM, preferably in aconcentration of from 1.5 to 2.0 mM, and more preferably in aconcentration of approximately 1.8 mM because the medium alreadycontains 1.8 mM of calcium. Likewise, the calcium concentration to beadded to achieve the desired concentration necessary for implementingthe culturing method of the present invention can be readily calculatedin consideration of the calcium concentration of a medium itself, takenfrom among typical media.

In the culture medium of the present invention, magnesium is employed toprevent the precipitation of calcium. Magnesium may be used in aconcentration of from 1.0 to 3.0 mM in the medium, and preferably in aconcentration of approximately 1.8 mM. For example, when magnesium ispresent in a concentration of less than 1.0 mM in the culture medium,calcium is apt to precipitate. On the other hand, a magnesiumconcentration higher than 3.0 mM in the culture medium is likely toblock the formation of the extracellular matrix (ECM), interfere withthe adherence of the cells to the bottom of the culture dish, thusrendering them susceptible to shear stress, and increase intracellularmineralization. For instance, when α-MEM is adopted as the culturemedium, magnesium may be added in a concentration of from 0.2 to 2.2 mM,and preferably in a concentration of 1.0 mM because the medium alreadycontains 0.8 mM magnesium. Likewise, the magnesium concentration to beadded to achieve the desired concentration necessary for implementingthe culturing method of the present invention can be readily calculatedin consideration of the magnesium concentration of a medium itself,taken from among typical media.

Thus, the culture medium according to a preferred embodiment of thepresent invention may be based on α-MEM supplemented with 5 to 30% offetal bovine serum (FBS), 0.3 to 2.0 mM of calcium, and 0.2 to 2.2 mM ofmagnesium, thus calcium and magnesium amounting to a total of from 2.1to 3.8 mM, and from 1.0 to 3.0 mM, respectively.

Furthermore, another feature of the culturing method of the presentinvention is a hypoxic culturing condition for mesenchymal stem cells.Compared to a normoxic condition, the hypoxic condition promotes theproliferation of mesenchymal stem cells, with the suppression ofimmunogenicity and the stimulation of cytokine secretion. In thiscontext, the hypoxic condition is an atmosphere with an oxygen contentof from 2 to 5%. A problem with an oxygen concentration below 2% or over5% is a significant decrease in the proliferation of mesenchymal stemcells. In one preferred embodiment of the present invention, mesenchymalstem cells are cultured in an atmosphere of approximately 3% oxygen. Thehypoxic condition may be achieved by adjusting the oxygen concentrationof a cell incubator. For example, an incubator may be purged withnitrogen (100%) or nitrogen/carbon dioxide (95%/5%) to adjust thenormoxic atmosphere into a hypoxic atmosphere. The oxygen concentrationin an incubator may be monitored by an oxygen sensor installed on theincubator.

Except for the aforementioned conditions of the present invention,mesenchymal stem cells may be cultured in a conventional manner. Forexample, mesenchymal stem cells may be cultured in a three-dimensionalbioreactor or spinner or a typical adherent culture vessel.

When the primary feature for the concentration of calcium and magnesiumis combined with the secondary feature for the hypoxic condition, asynergistic effect can be obtained. That is, a combination of theconcentration of calcium and magnesium and the hypoxic condition allowsmesenchymal stem cells to proliferate more efficiently, with a higherimprovement in the suppression of immunogenicity and the stimulation ofcytokine secretion, compared to the individual conditions. For example,under the combined conditions, mesenchymal stem cells proliferate 1.5-to 5-fold further, with a 1- to 3-fold decrease in immunogenicity, and a1.5- to 3-fold increase in cytokine secretion, compared to individualconditions. The combined condition for the culturing method of thepresent invention is referred to as “CMH condition”(calcium+magnesium+hypoxia condition).

The culturing method of the present invention may be applied to passagesof mesenchymal stem cells. In other words, the mesenchymal stem cellscultured using the culturing method of the present invention can besub-cultured in the same manner. By allowing mesenchymal stem cells toproliferate more efficiently, the culturing method of the presentinvention has the advantage of producing a greater number of mesenchymalstem cells even though fewer passages are performed. For instance, after5 passages in which the same number of cells were inoculated andcultured for a uniform duration at each passage, the culturing method ofthe present invention was found to produce mesenchymal stem cells 100-to 1,000-fold greater in number than that of conventional methods.

In addition, the mesenchymal stem cells grown by the culturing method ofthe present invention are not only non-immunogenic so that they cause noimmune responses, but can also be effectively used as a cell therapeuticagent or cartilage regenerating agent for humans.

Thus, contemplated in accordance with another aspect of the presentinvention are mesenchymal stem cells, prepared using the culturingmethod, that are improved in proliferative capacity, viability, recoveryrate, and immunological property. The improvement in immunologicalproperty includes non-immunogenicity, the release of animmunosuppressant (e.g., PGE₂) to suppress immunity, and the increasedrelease of useful cytokines (e.g., Tsp-2).

In accordance with a further preferred embodiment, the present inventionprovides a cell therapeutic agent comprising the mesenchymal stem cells.The cell therapeutic agent of the present invention finds applicationsin the regeneration or protection of adipocytes, osteocytes,chondrocytes, myocytes, neurocytes, cardiomyocytes, hepatocytes, isletbeta cells, vascular cells, or pneumocytes. In addition, the celltherapeutic agent of the present invention is useful for one selectedfrom the group consisting of the treatment of pulmonary diseases; thesuppression or treatment of lung disease-induced inflammation; theregeneration of pulmonary tissues; and the suppression of pulmonaryfibrosis. Particularly, it can be used to suppress or improve pulmonarydisease-induced inflammation and fibrosis. Further, the cell therapeuticagent of the present invention can be applied to the therapy ofcardiovascular diseases or the regeneration of cartilage. Moreover, thecell therapeutic agent of the present invention can reduce immuneresponses, immune cell penetration, or immunogenicity; improveimmunomodulative functions; and suppress inflammatory reactions. Also,the cell therapeutic agent of the present invention is applied totherapy of autoimmune diseases, or graft-vs-host diseases.

The following Examples are provided to illustrate preferred embodimentsof the present invention, and are not intended to limit the scope of thepresent invention.

For use in the present invention, human cord blood-derived mesenchymalstem cells were obtained from Medipost Co. Ltd., Korea. The cells may beprepared by collecting umbilical cord blood, isolating mesenchymal stemcells from umbilical cord blood, and culturing the mesenchymal stemcells, as illustrated below.

Umbilical cord blood may be collected from the umbilical vein which isexpelled out of the uterus either while the placenta remains within theuterus after normal spontaneous vaginal delivery or once the placentahas been expelled from the uterus after cesarean section.

After neonatal birth, the umbilical vein which is expelled from theuterus and by which the newborn is connected to the placenta must beaseptically treated before collecting umbilical cord blood therefrom.

Umbilical cord blood is withdrawn from the umbilical vein into a bagcontaining an anticoagulant through a syringe.

Methods of isolating mesenchymal stem cells from umbilical blood andculturing the cells are disclosed in Korean Patent No. 10-0494265, andmany reports (Pittinger M F, Mackay A M, et al., Science, 284: 143-7,1999; Lazarus H M, Haynesworth S E, et al., Bone Marrow Transplant, 16:557-64, 1995). One of them is briefly described below.

Monocytes are separated by centrifuging the collected umbilical cordblood and washed several times to remove impurities therefrom. Then, themonocytes are seeded at a proper density into a culture vessel andallowed to grow with the formation of a single layer. Mesenchymal stemcells are morphologically homogeneous and grow while forming coloniescomprising spindle-shaped cells, as observed under a phase-contrastmicroscope. Then, the cells are cultured with passage upon confluenceuntil a necessary number of cells are obtained.

Example 1: Proliferative Capacity of Umbilical Cord Blood-DerivedMesenchymal Stem Cells According to Calcium Concentration

To examine the proliferative capacity thereof according to calciumconcentration, umbilical cord blood-derived mesenchymal stem cells werecultured in the presence of various concentrations of calcium.

Umbilical cord blood-derived mesenchymal stem cells (MSC #1 and #2)which had been collected after delivery with the informed consent ofdifferent mothers and stored in a frozen state were thawed, and culturedat 37° C. in α-MEM (Invitrogen, USA) supplemented with 10% FBS under a5% CO₂ condition in an incubator (hypoxia/CO₂ incubator, ThermoScientific #3131). When the cells were grown to 80˜90% confluency, theywere separated into single cells by treatment with trypsin. To α-MEM(supplemented with 10% FBS; containing 1.8 mM calcium and 0.8 mMmagnesium), various concentrations (0 mM, 1.5 mM, 3 mM, 4.5 mM, 6 mM,and 7.5 mM) of calcium were added so that the calcium concentrations ofthe medium was adjusted into: 1.8 mM, 3.3 mM, 4.8 mM, 6.3 mM, 7.8 mM,and 9.3 mM. The mesenchymal stem cells were inoculated at a density of5,000 cells/cm² into the media. In order to prevent calcium-inducedprecipitation, magnesium was added in a concentration of 1 mM to eachmedium (containing a total magnesium concentration of 1.8 mM). The cellswere cultured in a 21% (v/v) oxygen (normoxia) condition, with passagesupon 80˜90% confluency. They were counted every passage, using aCELLOMETER® Auto T4 cell counter (Nexelcom, Lawrence, Mass., USA). Theresults are given in FIG. 1A through FIG. 1D. FIG. 1A, FIG. 1B, FIG. 1C,and FIG. 1D are graphs showing cell count folds relative to the seededcell count at 7 days (FIG. 1A and FIG. 1C) and cumulative cell countsuntil 21 days (FIG. 1B and FIG. 1D) after umbilical cord blood-derivedmesenchymal stem cells derived from two different sources (MSC #1 and#2) were cultured in α-MEM to which calcium was further added in variousconcentrations of from 0 to 7.5 mM.

As can be seen in FIG. 1A, through FIG. 1D, the proliferative capacityof the cells peaked when calcium was further added in a concentration of1.5 mM (a total calcium concentration of 3.3 mM), which was alsoobserved in the same pattern over passages. Upon the addition of 3 mM orhigher calcium (a total calcium concentration of 4.8 mM or higher inmedia), the proliferative capacity was gradually decreased.

In order to determine an optimal calcium concentration, calcium wasadded in further fractioned concentrations to the maximum of 3 mM. Theresults are shown in FIG. 2A through FIG. 2D. FIG. 2A, FIG. 2B, FIG. 2C,and FIG. 2D are graphs showing cell counts after umbilical cordblood-derived mesenchymal stem cells derived from two different sources(MSC #1 and #2) were cultured for 7 days in the presence of a totalcalcium concentration of 1.8 mM, 2.1 mM, 2.4 mM, 2.7 mM, 3.0 mM, 3.3 mMand 3.6 mM (FIG. 2A and FIG. 2C), and for 6 days in the presence of atotal calcium concentration of 1.8 mM, 3.4 mM, 3.6 mM, 3.8 mM, 4.0 mM,4.2 mM, and 4.4 mM (FIG. 2B and FIG. 2D).

As can be seen in the graphs, the proliferative capacity increased overan added calcium concentration range from 0 to 1.8 mM (totalconcentrations of from 1.8 to 3.6 mM in media), and then started todecrease when the added calcium concentration exceeded 1.8 mM (a totalcalcium concentration of 3.6 mM in media). From these results, it isunderstood that the optimal calcium concentration for allowing themaximal proliferation of mesenchymal stem cells is 3.6 mM in a medium.Thus, it is advantageous in terms of proliferative capacity thatmesenchymal stem cells are cultured in a typical medium containingcalcium preferably in a concentration of from 2.1 to 4.3 mM, and morepreferably in a concentration of from 3.3 to 3.8 mM.

Example 2: Proliferative Capacity of Umbilical Cord Blood-DerivedMesenchymal Stem Cells According to Oxygen Concentration

To examine the proliferative capacity thereof according to oxygenconcentration, umbilical cord blood-derived mesenchymal stem cells werecultured in the presence of various concentrations of oxygen.

Specifically, umbilical cord blood-derived mesenchymal stem cells werecultured in the same manner as in Example 1 under 3% or 5% oxygen, orunder a normoxic (oxygen level 21% in air) condition, with the exceptionthat neither calcium nor magnesium was further added to a 10%FBS-supplemented α-MEM. The results are given in FIG. 3A through FIG.3D. FIG. 3A, FIG. 3B, FIG. 3C, and FIG. 3D are graphs showing times ittook for the cells to double in number when umbilical cord blood-derivedmesenchymal stem cells derived from two different sources (MSC #1 and#2) were cultured under various oxygen conditions (normal, 3% and 5%)after 1, 2 and 3 rounds of passage (FIG. 3A and FIG. 3C), and cumulativecell counts until 21 days after the umbilical cord blood-derivedmesenchymal stem cells were cultured under the oxygen conditions (FIG.3B and FIG. 3D).

As can be seen in these graphs, the proliferative capacity was measuredto be higher under the hypoxic conditions than the normoxic conditions,although there were differences between batches. Particularly, theproliferative capacity peaked at an oxygen level of 3%, which wasobserved in the same pattern for the cells which had been cultured withmany rounds of passage. In addition, the cells were examined forproliferative capacity under further fractioned oxygen conditions to amaximum of 5%. An oxygen level of from 2 to 5% was preferred (data notshown).

Example 3: Proliferative Capacity of Umbilical Cord Blood-DerivedMesenchymal Stem Cells According to Combination of Calcium (Inclusive ofMagnesium) and Oxygen Conditions

An examination was made of the proliferative capacity of umbilical cordblood-derived mesenchymal stem cells according to combinations ofcalcium (inclusive of magnesium) and oxygen concentration conditions.The cells were cultured in a typical condition (control), in thepresence of externally added calcium (inclusive of magnesium), in ahypoxic condition, and in an externally added calcium (inclusive ofmagnesium)/hypoxia condition (hereinafter referred to as “CMH”). In thisregard, the media contained calcium and magnesium at totalconcentrations of 3.6 and 1.8 M, respectively (1.8 mM calcium and 1 mMmagnesium additionally added). The hypoxic condition was set forth at anoxygen level of 3%. The cells were cultured in a manner similar to thatof Example 1. After 5 passages (P5) in a typical condition, themesenchymal stem cells were cultured with 7 rounds of passages (P12) inthe CMH condition at regular intervals of 7 days between passages.

The results are given in FIG. 4A and FIG. 4B. FIG. 4A and FIG. 4B showdoubling times (day) of the cells (FIG. 4A), and cumulative cell counts(FIG. 4B) after passages under the conditions.

As is understood from the data of FIG. 4A and FIG. 4b , theproliferative capacity of the cells was significantly increased whenthey were cultured in the CMH condition, compared to a hypoxic conditionor a calcium addition condition. This effect was observed in the samepattern over many rounds of passage. Experiments with various batches ofcells showed similar results although there were differences to somedegree. Thus, these results demonstrate that the CMH condition of thepresent invention is very effective for proliferating umbilical cordblood-derived mesenchymal stem cells.

Example 4: Viability and Recovery Rate of Umbilical Cord Blood-DerivedMesenchymal Stem Cells According to Culture Condition

An examination was made of the effect of the CMH condition of thepresent invention on the viability and recovery rate of umbilical cordblood-derived mesenchymal stem cells. For this, umbilical cordblood-derived mesenchymal stem cells (MSC #1) were cultured in a typicalcondition (control), in a hypoxic condition (3%), in an increasedcalcium condition (1.8 mM; a total calcium level of 3.6 mM in a medium),and in a CMH condition (3% O₂+1.8 mM calcium added+1 mM magnesiumadded), detached from culture vessels, and washed three times with andsuspended in a fundamental medium (α-MEM). While being maintained atroom temperature, the cell suspensions were examined for viability andrecovery rate with time. Cell viability was expressed as a percentage oflive cells to dead cells after the cells collected and suspended in afundamental medium were stained with trypan blue and total cellsincluding live cells stained blue in a predetermined volume (10˜20 μL)of the suspension were counted using a hemocytometer. The recovery ratewas expressed as a percentage of live cell counts post-culture topre-culture.

The results are given in FIG. 5. FIG. 5 shows cell viability (uppergraph) and recovery rates (lower graph) one and two days after umbilicalcord blood-derived mesenchymal stem cells were cultured in theconditions.

As can be seen in FIG. 5A and FIG. 5B, the cells were observed toexhibit higher viability and recovery rate when they were cultured in ahypoxic condition or an increased calcium condition than in a typicalcondition, and even higher viability and recovery rate when they werecultured in the CMH condition. The same results were obtained withumbilical cord blood-derived mesenchymal stem cells derived fromdifferent sources although there were a difference therebetween to somedegree. These data, taken together, indicate that the CMH condition isadvantageous over a typical condition, or the individual conditions, inincreasing the viability of umbilical cord blood-derived mesenchymalstem cells to recover a greater number of cells.

Mesenchymal stem cells (MSC #1 to #4) were cultured with passage in atypical condition and in the CMH condition, and examined forproliferative capacity. The results are given in FIG. 6A through FIG. 6Dwhich show doubling time (FIG. 6A and FIG. 6C) and cumulative cellcounts (FIG. 6B and FIG. 6D).

As can be seen in the graphs, the CMH condition significantly reducedthe doubling time, an index for cell proliferation, over many rounds ofpassage, compared to the control. In addition, as is apparent from thedata of the cumulative growth curves, a much greater number ofmesenchymal stem cells, even though derived from the same source, wereobtained in the CMH condition. The same results were obtained fromexperiments with different umbilical cord blood-derived mesenchymal stemcells although there was a difference therebetween to some degree. Thesedata indicate that the CMH condition induces mesenchymal stem cells toproliferate with better efficiency. Particularly, an even greater numberof mesenchymal stem cells were produced when the CMH condition wasapplied to an initial passage of umbilical cord blood-derivedmesenchymal stem cells.

Example 5: Assay for Stemness and Senescence of Umbilical CordBlood-Derived Mesenchymal Stem Cells According to Culture Condition

To examine why the CMH condition improves the proliferation of umbilicalcord blood-derived mesenchymal stem cells, their stemness andsenescence, which are associated with the proliferation of stem cells,were assayed.

For this, umbilical cord blood-derived mesenchymal stem cells werecultured in a typical condition and in the CMH condition, as in Example3. The cells were detached with trypsin when they reached 80-90%confluency. After removal of the media by centrifugation, the cells werewashed with PBS and recovered by centrifugation. This procedure wasrepeated twice to completely remove media from the cells. Subsequently,RNA was isolated using an RNA isolation kit (Invitrogen) according tothe protocol of the manufacturer. The RNA was reverse transcribed intocDNA in the presence of the reverse transcriptase SuperScript™III(Invitrogen). Real-time PCR was carried out on the cDNA using primersspecific for the stemness markers Oct4 and nanog, the senescence markerP16, and GADPH. The PCR started with denaturation at 95° C. for 10 min,and was performed with 30 cycles of 95° C. for 10 sec, 62° C. for 30sec, and 72° C. for 10 sec in a LIGHTCYCLER® 480 Real-Time PCR Systeminstrument (Roche).

TABLE 1 Primers for RT-PCR Marker Sequence (F: forward, R: reverse) Oct4F; CAATTTGCCAAGCTCCTGA (SEQ ID NO: 1)R; CGTTTGGCTGAATACCTTCC (SEQ ID NO: 2) NanogF; AGATGCCTCACACGGAGACT (SEQ ID NO: 3)R; TTTGCGACACTCTTCTCTGC (SEQ ID NO: 4) P16F; GTGGACCTGGCTGAGGAG (SEQ ID NO: 5)R; CTTTCAATCGGGGATGTCTG (SEQ ID NO: 6) GADPHF; AGCCACCATCGCTCAGACAC (SEQ ID NO: 7)R; GCCCAATACGACCAAATCC (SEQ ID NO: 8)

The levels of RNA obtained by the RT-PCR were normalized to that ofGAPDH before the expression levels of RNA for each marker in the cellscultured in the typical condition and the CMH condition were compared(relative analysis, ddCT method).

The results are given in FIG. 7A and FIG. 7B. FIG. 7A and FIG. 7B showmRNA expression levels of two different umbilical cord blood-derivedmesenchymal stem cells (MSC #1 and #2).

As can be seen in FIG. 7A and FIG. 7B, the expression levels of thestemness markers Oct4 and nanog were higher in the umbilical cordblood-derived mesenchymal stem cells cultured in the CMH condition thanin a typical condition (control) and than in individual conditions. Thesenescence marker P16 showed an inverse expression pattern to that ofOct4. These results indicate that the CMH condition maintains thestemness of mesenchymal stem cells while suppressing the senescence,thus improving proliferative capacity.

To confirm the ability of the CMH condition to suppress the senescenceof mesenchymal stem cells, the following experiments were carried out.Umbilical cord blood-derived mesenchymal stem cells were cultured in atypical condition and in the CMH condition as in Example 3, with 7-8passages. After removal of the media, the cells were washed once withPBS, and incubated at room temperature for 3-5 min with 1 mL of a 1×fixation solution (Cell Signaling Technology). The fixation solution wasremoved from the cells which were then washed twice with 2 mL of PBS.Subsequently, the cells were incubated for 2 to 24 hrs with 1 mL of adye solution for β-galactosidase (Cell Signaling Technology) in a 37° C.incubator. After removal of the dye solution therefrom, the cells werewashed with 1 mL of PBS, and the resulting stained senescent cells werecounted under the inverted microscope ECLIPSE TE2000-U (Nikon Co.,Kanagawa, Japan).

The results are given in FIG. 8A and FIG. 8B. FIG. 8A and FIG. 8B showmicrophotographs of cells after staining with SA-β-gal (FIG. 8A), andgraphs of SA-β-gal activity (FIG. 8B). The SA-β-gal activity wasdetermined by calculating the ratio of stained cells to total cellscounted on a photograph taken at 40-−100-fold magnification

As is apparent from FIG. 8A and FIG. 8B, the progression of senescencein the mesenchymal stem cells was retarded further in the CMH conditionthan in the calcium addition condition or the hypoxic condition, andmuch further than in the typical condition.

Taken together, the data obtained above demonstrate that the CMHcondition of the present invention maintains stemness and suppressessenescence more efficiently than do the typical conditions or theindividual conditions, whereby the mesenchymal stem cells canproliferate with high efficiency.

Example 6: Differentiation Potential and Maker Expression of UmbilicalCord Blood-Derived Mesenchymal Stem Cells According to Culture Condition

An examination was made of the effect of the CMH condition on theproperty of umbilical cord blood-derived mesenchymal stem cells. To thisend, mesenchymal stem cells were assayed for differentiation potentialand marker expression by chondrogenic induction and osteogenicinduction.

Umbilical cord blood-derived mesenchymal stem cells obtained from twodifferent sources (MSC #1 and #2) were cultured in a typical condition(control) and in the CMH condition, as in Example 3, before they wereinduced to differentiate into cartilage and bone, as follows. Then,differentiation into cartilage and bone was evaluated using a stainingmethod.

Chondrogenic Induction

For use in chondrogenic induction, cells were placed in a population of2-2.5×10⁵ cells in a 15 mL conical tube, and centrifuged to give a cellpellet. It was washed with D-PBS and suspended in 200-250 μl of adifferentiation medium [high glucose DMEM (Gibco, cat #. 11995), 10ng/ml TGFβ-3 (Sigma, cat #. T5425, 2 μg), 500 ng/ml BMP-6 (R&D, cat #.507-BP, 20 μg), 50 μg/ml ascorbic acid (Sigma, cat #. A8960), 50 mg/ml(1:100) ITS™+Premix (BD, cat #. 354352), 40 μg/ml L-proline (Sigma, cat#. P5607), 100 μg/ml sodium pyruvic acid (Sigma, cat #. P8574), 100 nMdexametasone (Sigma, cat #. D2915)], and the cell suspension wasaliquoted into tubes. These tubes were centrifuged at 1,500 rpm for 5min, after which the cells were cultured for 4 weeks in a 37° C. CO₂incubator, with the tubes opened slightly, to induce differentiationinto cartilage. The differentiation medium was substituted by half witha fresh one, twice a week.

Cartilage Staining Protocol

After the chondrogenic induction, the cells were centrifuged, washedwith PBS, and fixed at room temperature for 0.5 to 1 hr in 4%paraformaldehyde. Subsequently, the cells were washed two or three timeswith distilled water, and prepared into sections (4-5 μm thick) using acryosection method. The sections were immersed for 3-5 min in 95%ethanol, and washed twice with water. After being stained for 7 min with0.1% safranin 0, the cells were washed twice with 70% ethanol, once with70% ethanol, twice with 95% ethanol, once with 95% ethanol, and twicewith 100% ethanol, immersed for 3 min in a xylene substrate solution,and dried. Thereafter, the stained cells were covered with alipid-soluble mounting solution and observed. The chondrogenic inductionwas evaluated by comparing the color (violet), the size ofdifferentiated pellets, and the lacuna structure formed.

Osteogenic Induction

For use in osteogenic induction, the cells were plated at a density500-1000 cells/well into 6-well plates, and 2˜4 days later, the mediumwas substituted with an osteogenic induction medium (β-glycerolphosphate 2.1604 g, L-ascorbic acid-2-phosphate 0.012805 g,dexamethasone/UVAB 0.6 mg, gentamycin (10 mg/ml) 5 ml and FBS 100 ml in1 L of α-MEM). The cells were cultured for 2-3 weeks with thedifferentiation medium substituted with a fresh one every three days.The chondrogenic induction was evaluated by an ALP staining method.

Bone Staining Protocol

The differentiated cells were washed twice with PBS and incubated for30˜45 sec in a fixation solution (40% acetone). They were washed againtwo or three times with distilled water and incubated for 30 min with analkaline staining solution (Fast violet B salt) in a dark place. Then,the cells were washed twice with distilled water, and treated for 10-20sec with Mayer's hematoxylin solution. After removal of the stainingsolution therefrom, the cells were washed with tap water, dried, coveredwith a lipid-soluble mounting solution, and observed. Becauseosteoblasts are stained dark brown due to the activation ofintracellular alkaline phosphatase, the chondrogenic induction wasevaluated by the degree of staining.

The results are given in FIG. 9A and FIG. 9B. As can be seen in FIG. 9Aand FIG. 9B, there were no significant differences in chondrogenicinduction and genic induction between the mesenchymal stem cellscultured in the typical condition and in the CMH condition.

Meanwhile, immunophenotypes of the cell surface antigens on theumbilical cord blood-derived mesenchymal stem cells cultured accordingto the method of the present invention were examined. In this context,the expression of the surface markers (CD34, CD73, CD45, and CD105) wasanalyzed using FACS.

Umbilical cord blood-derived mesenchymal stem cells cultured in atypical condition and in the CMH condition were trypsinized, and washedthree times with PBS containing 2% FBS. They were reacted with thehematopoietic cell-associated antigens CD34 and CD45, both conjugatedwith FITC (fluorescein isothiocyanate), the immunomodulation-associatedantigen CD73 conjugated with PE (phycoerythrin), and theangiogenesis-associated antigen CD105 conjugated with PE. Afterwards,the cells were additionally marked with a secondary antibody (IgG-FITC;Jackson ImmunoResearch, West Grove, Pa., USA) in a manner similar toWestern blotting, followed by detecting the signal of the secondaryantibody using FACS to ratios of the cells expressing the markers tototal cells. After the reaction, the signals were analyzed using aFACSCALIBUR™ flow cytometer (Becton Dickinson, San Jose, Calif., USA),and the software CELLQUEST.

The results are summarized in Table 2, below.

TABLE 2 CD34 CD73 CD45 CD105 MSC #1 Control − + − + CMH − + − + MSC #2Control − + − + CMH − + − + MSC #3 Control − + − + CMH − + − +

As is understood from the data of Table 2, there were no significantdifferences in the expression of marker proteins between cells culturedin the CMH condition and in the typical condition.

Taken together, the data obtained above demonstrate that the CMHcondition of the present invention has no significant influence on thefundamental properties of umbilical cord blood-derived mesenchymal stemcells.

Example 7: Comparison of Immunogenicity and Immunosuppression ofUmbilical Cord Blood-Derived Mesenchymal Stem Cells According to CultureCondition

Immunological properties of umbilical cord blood-derived mesenchymalstem cells according to culture conditions were evaluated using a mixedlymphocyte reaction (MLR) as follows.

For a negative control, umbilical cord blood-derived mesenchymal stemcells cultured in the presence of 10 μg/ml mitomycin C (Sigma-Aldrich,St Louis, Mo., USA) in a typical condition and in the CMH condition wereseparately seeded at a density of 2×10⁴ cells/well into 96-well plates,responding cells (peripheral blood monocytes (expressed as “A”);ALLCELLS, Emeryville, Calif.) at a density of 1×10⁵ cells/well, andstimulator cells (unrelated peripheral blood monocytes (expressed as“B”); ALLCELLS, Emeryville, Calif.) at a density of 1×10⁵ cells/well. Asa positive control (1), peripheral blood monocytes treated with 10 μg/mlPHA-L (expressed as “H”; Roche Diagnostics GmbH, Mannheim, Germany) wereadded at a density of 1×10⁵ cells/well to 96-well plates. For a positivecontrol (2), each of the responding cells and the stimulator cells wereadded at a density of 1×10⁵ cells/well. In a test group, mesenchymalstem cells were incubated with peripheral blood monocytes,PHA-L-stimulated peripheral blood monocytes, or a combination of theresponding cells and the stimulator cells, each monocyte being used at adensity of 1×10⁵ cells, for 5 days, and the proliferation and colonyformation of the responding cells were observed under a microscope. Onday 5 after incubation, the cells were treated with BrdU (BD Bioscience,San Jose, Calif., USA) so that levels of the DNA newly synthesized forthe previous 24 hrs in the responding cells were determined by measuringabsorbance at 370 nm on a VERSAmax™ microplate reader (Molecular DevicesCo., Sunnyvale, Calif., USA).

The results are shown in FIG. 10A and FIG. 10B. As can be seen in FIG.10A and FIG. 10B, the proliferation was induced in thePHA-L(H)-stimulated unrelated peripheral blood monocytes (A+H) whereasumbilical cord blood-derived mesenchymal stem cells did not stimulatethe responding cells, thus resulting in no induction of cellproliferation (hUCB-MSC+A). Particularly, the umbilical cordblood-derived mesenchymal stem cells were observed to have greaterinhibitory effects on the proliferation of the responding cells whenthey were cultured in the CMH condition than in a typical condition.These data indicate that the umbilical cord blood-derived mesenchymalstem cells cultured in the CMH are less apt to be immunogenic than arethose cultured in a typical condition.

When applied to the situation in which the immune response was inducedby a reaction between the responding cells (A) and the stimulator cells(B), i.e., (A+B), or by the artificial stimulation of the respondingcells (A) with PHA-L, i.e., (A+H), the umbilical cord blood-derivedmesenchymal stem cells cultured in the CMH condition were observed tosuppress the proliferation of the responding peripheral blood monocytesmore greatly than did those cultured in the typical condition. Similarresults were obtained with umbilical cord blood-derived mesenchymal stemcells obtained from different sources although there was a difference tosome, but slight degree. These data demonstrate that the CMH culturecondition is advantageous over typical conditions in terms of thesuppression of immunogenicity.

After the mesenchymal stem cells were reacted in the same manner asdescribed above, PGE₂ (prostaglandin E₂), an immunosuppressant, releasedtherefrom was analyzed using a PGE2 ELISA kit (Cayman, Ann Arbor, Mich.,USA) according to the protocol of the manufacturer. The cultures fromthe MLR were used as specimens.

Standards necessary for ELISA assay were prepared to have a maximumdensity of 1,000 pg/mL, with a minimum density of 7.8 pg/mL seriallyhalf-diluted from the maximum. Each of the standards and the culturesupernatants of the test group was added in an amount of 50 μl to eachwell of PGE₂ capture antibody-coated plates. Then, 50 μl of the PGE₂AchE tracer and 50 μl of a primary antibody were added to each well,followed by incubation at 4° C. for 18 hrs. The plates were washed fivetimes with a wash buffer, and 200 μl of Ellman's reagent (includedwithin the kit), was added to each well, followed by the addition of 5μl of the tracer per well. The plates were incubated for 60-90 min in adark condition, and absorbance was read at 450 nm.

The results are given in FIG. 11A and FIG. 11B. As can be seen in FIG.11A and FIG. 11B, the umbilical cord blood-derived mesenchymal stemcells were observed to release PGE₂ in an approximately 3.7-fold greateramount when cultured in the CMH condition than in a typical condition.Similar results were obtained with different umbilical cordblood-derived mesenchymal stem cells. These data demonstrate that theumbilical cord blood-derived mesenchymal stem cells cultured in the CHMcondition were more immunosuppressant than those cultured in a typicalcondition.

Example 8: In Vitro Assay for Ability of Umbilical Cord Blood-DerivedMesenchymal Stem Cells to Release Cytokines According to CultureCondition

Effects of culture conditions on the ability of umbilical cordblood-derived mesenchymal stem cells to release cytokines were assayedby measuring Tsp-2 released during the differentiation of the umbilicalcord blood-derived mesenchymal stem cells into chondrocytes.

Umbilical cord blood-derived mesenchymal stem cells were cultured in atypical condition (control) and in the CMH condition in the same manneras in Example 3. When reaching 80-90% confluency, they were detached bytreatment with trypsin. After centrifugation, the cell pellets werewashed with high glucose DMEM containing 40 μg/ml L-proline, 0.6 μg/mldexamethasone, 50 μg/ml ascorbic acid, and 100 μg/ml sodium pyruvate, tocompletely remove FBS from the cells. The umbilical cord blood-derivedmesenchymal stem cell pellets obtained again by centrifugation weresuspended at a density of 2.0×10⁵ cells/400 μl, and placed in an aliquotof 400 μl in 15 mL conical tubes. Following centrifugation at 550×g for5 min, the tubes were so very loosely closed. The tubes were incubatedfor 24 hrs while being placed upright in a rack. Once a pellet wasformed, the supernatant was collected and analyzed for the level ofTsp-2 using a Tsp-2 assay kit (R&D systems, USA).

The results are given in FIG. 12. Tsp-2 is a factor accounting for thetiter of umbilical cord blood-derived mesenchymal stem cells for use asa cartilage regenerating agent. Cells that released a higher level ofTsp-2 were evaluated to regenerate cartilage more effectively. As isapparent from the data of FIG. 12, all of four different umbilical cordblood-derived mesenchymal stem cells released higher levels of Tsp-2 inthe CMH condition than in a typical condition.

Taken together, the data obtained above indicate that the umbilical cordblood-derived mesenchymal stem cells cultured in the CMH condition haveexcellent potential of differentiating into chondrocytes and are thususeful as a cartilage regenerating agent.

What is claimed is:
 1. A method for treating or improving a pulmonarydisease, comprising administering a cell therapeutic agent comprisingmesenchymal stem cells to a subject in need thereof, wherein saidmesenchymal stem cells are obtained by a culture method comprising: (a)culturing mesenchymal stem cells in a medium containing calcium in aconcentration of from 2.7 to 3.8 mM and magnesium in a concentration offrom 1.0 to 3.0 mM under a hypoxic condition of 2 to 5% oxygen.
 2. Themethod of claim 1, wherein the mesenchymal stem cells of (a) are derivedfrom umbilical cord blood, bone marrow, lipid, muscle, skin, amnioticfluid, umbilical cord, or teeth.
 3. The method of claim 1, wherein themedium is selected from the group consisting of a Dulbecco's modifiedeagle medium (DMEM), a minimal essential medium (MEM), an α-MEM, aMcCoys 5A medium, an eagle's basal medium, a CMRL (Connaught MedicalResearch Laboratory) medium, a Glasgow MEM, a Ham's F-12 medium, anIscove's modified Dulbecco's medium (IMDM), a Leibovitz's L-15 medium,an Roswell Park Memorial Institute (RPMI) 1640 medium, a medium 199, anda Hank's medium
 199. 4. The method of claim 3, wherein the mediumcomprises 5 to 30% of fetal bovine serum.
 5. The method of claim 3,wherein the medium does not comprise fetal bovine serum, but a serumreplacement.
 6. The method of claim 1, wherein the medium is based on anα-MEM supplemented with 5 to 30% of fetal bovine serum (FBS), 0.3 to 2.0mM of calcium, and 0.2 to 2.2 mM of magnesium.
 7. The method of claim 1,wherein the culture method further comprises sub-culturing themesenchymal stem cells obtained in (a) in the same condition as inclaim
 1. 8. The method of claim 1, wherein the medium of (a) comprisescalcium in a concentration of from 3.3 to 3.8 mM.